Design docs: Clarify unrelated topics as optional

Change-Id: Id879ba33c5b0c6ece529a30b2f0dcd52d880e5eb
diff --git a/Documentation/dev-design-docs.txt b/Documentation/dev-design-docs.txt
index 5e3f7a9..b4ba10b 100644
--- a/Documentation/dev-design-docs.txt
+++ b/Documentation/dev-design-docs.txt
@@ -58,8 +58,9 @@
 * All possible solutions are fairly discussed with their pros and cons,
   and treated equally until a conclusion is made.
 * Unrelated issues (judged by the design doc owner) that are identified
-  during discussions are extracted into new design docs (initially
-  consisting only of an `index.md` and a `use-cases.md` file).
+  during discussions may be extracted into new design docs (initially
+  consisting only of an `index.md` and a `use-cases.md` file). Doing so
+  is optional yet can be done by either the design owner or reviewers.
 * Changes making iterative improvements can be submitted frequently
   (e.g. additional uses-cases can be added later, solutions can be
   submitted without describing implementation details, etc.).